ST. LOUIS — One thing to count on in the second presidential debate Sunday night: a torrent of falsehoods and half-truths, so many, so fast that not even the most diligent open-minded voter could sort through it.

As it turns out, most voters aren't open minded. They're tribal. They don't flinch when they hear an untruth from the team they back.

Donald Trump's supporters don't believe he lies or don't care. And Hillary Clinton's backers just as readily dismiss concerns about her veracity.

"The people who've made up their minds overlook the flaws," said James Thurber, former director of American University's Center for Congressional and Presidential Studies. He edited the 2015 book American Gridlock: The Sources, Character and Impact of Political Polarization.

It's akin to the phenomenon on display since Friday's blockbuster revelation of a 2005 video in which Trump talks about grabbing women's genitals uninvited, and getting away with it because he's a star. Though some supporters denounced him, even calling on him to leave the race, others dug in, defending his vulgarity as frat-boy antics.

Misstatements have hurt many a candidate. Libertarian nominee Gary Johnson's credibility went up in smoke last month when he couldn't recognized "Aleppo" as the city at the heart of the Syrian conflict. President Gerald Ford asserted in a 1976 debate that there was "no Soviet domination in Eastern Europe," a gaffe dispelled by his own staff and belied by the Russian tanks in Poland.

Those were momentary stumbles.

Trump has shown a penchant for repeating falsehoods over and over, long after they've been debunked, a willingness to ignore facts that independent scorekeepers and scholars view as egregious.

"We're just in a different universe now with so many distortions on facts, especially on the Trump side," Thurber said.

Most partisans, like this Donald Trump backer in Nevada, are eager to point out the other candidate's falsehoods.

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The average voter has neither the time nor inclination to research every claim made in a presidential debate.

And many aren't even looking for accuracy or even consistency. They want leadership, reassurance, connection, an agenda that jibes with their own. They're not keeping score, assertion by assertion. It's more impressionistic.

It's not that they value dishonesty. It's just not their focus.

The disconnect shows up outside politics and it isn't confined to one side of the political spectrum. Researchers point to strong but unsubstantiated beliefs about the dangers of vaccines and genetically modified foods, for instance.

It's an apt analogy. The first Trump-Clinton debate drew 84 million viewers, but most weren't trying to make up their minds. They'd already picked a side.

"They're following a campaign like a sports fan and less like an idealized citizen" weighing the options, Nyhan said.

That gives the candidates leeway to exaggerate and falsify, to flip flop on trade deals or whether they supported the Iraq war, to downplay their mishandling of classified documents, to pretend they'd never made offensive comments about Mexicans and Muslims.

On Wednesday, for instance, Trump told a rally near Las Vegas that on Clinton's watch, the State Department "misplaced or lost $6 billion in taxpayer funds."

Here's what actually happened. In March 2014, the State Department's inspector general reported that paperwork related to $6 billion in contracts was missing or incomplete. "It's akin to spending $20 on lunch and losing or not asking for a receipt," as one fact-checker pointed out in June in a pants-on-fire ruling against Trump's repeated use of the allegation.

How is an ordinary debate watcher supposed to know things like that?

Trump's deep deficit when it comes to perceptions of trustworthiness comes from a blemished record throughout the 2016 campaign. Clinton's image problem stems from the 1990s, stoked by adversaries. Scandals involving Whitewater and the White House travel office gave way to concerns about Benghazi and deleted emails.

But partisans see past all that.

"Most people do put on partisan blinders," said Mark Mellman, a top Democratic pollster. "Most of them are looking at the debate and saying who seems to be connecting, who seems to be expressing the same values as me."

For anyone prone to conspiracy theories, life has never been easier. The internet is rife with validation from self-proclaimed authorities, or slanted "news" sites eager to feed anyone's appetite for misinformation.

"His supporters discount fact- checking because it's from a 'biased media' and an 'establishment elite,' " said Sean Theriault, a University of Texas government professor who has written books on partisan warfare and polarization.

"At the end of the day, on the big issues people are uncompromising, whether that's gay marriage, abortion or taxes," he said. "They would still rather go with their flawed candidate."

For those who prize integrity and accuracy in national leaders, there is hope.

While committed partisans hunker down and shrug off misinformation as the price of competition, the minority in the center — the tie-breaking voters who decide elections — generally lack an entrenched worldview.

And Trump's style has made him the most unpopular major-party nominee ever. If he loses, that will serve as a warning to future politicians.

Nyhan wonders how much worse it would be if fact checkers weren't ready to pounce, arguing that it's not fair to blame Trump's persistence on the referees' shortcomings.

"That's like saying firefighters have failed because there are still fires," he said. "Politicians have always spun and told half truths. That's never going to go away. But ... it's important to avoid normalizing this kind of pathological behavior."

Karlyn Bowman, a senior fellow at the conservative American Enterprise Institute, sees the focus on fact checking as so much "campaign noise" that voters mostly tune out.

"People rarely start with facts," she said. And that's OK, because the electorate's collective judgments is usually pretty good, even if it doesn't hinge on claims and counterclaims, or hours of studying briefing papers on climate policy and marginal tax rates.

"They're getting a sense of who these people are," she said. "Would I be comfortable with this person as president? Does he have the same kind of values that I do? That's what people see in a debate."

A growing partisan divide has only aggravated the tribal tendencies. A Pew Research Center survey last spring found the proportion on each side that holds a "very unfavorable" view of the other tripled since 1994.

"We've seen a rise in animosity or negativity toward the other side," said Pew's associate research director Jocelyn Kiley.

Trump and Clinton supporters of similar socioeconomic strata don't even agree on how well they're doing in the world. His perceive their lives are harder than those of people like them 50 years ago. Hers feel quite the opposite.

That's fertile ground for what social scientists and psychologists call "motivated reasoning."

"People listen to whatever's most consistent with their partisan beliefs. ... It makes it really hard to change people's minds," said Katherine Levine Einstein, co-author of the 2015 book Do Facts Matter? Information and Misinformation in Democratic Politics and a professor at Boston University.

Her research shows that the more closely a voter is paying attention, the more strongly they cling to beliefs, regardless of whether those beliefs are grounded in evidence, fact and reality.

"You would think that education would be protective against misinformation," she said. "It's not."